The present invention relates to apparatus and processes for indicating the general location of a movable member and further to a magnetic switch arrangement particularly useful in conjunction therewith. More particularly, the present invention is related to systems and processes for indicating the location of a movable member such as an overhead door and for correlating this position indicative to the relationship with respect to proximity of limits of travel for such doors. Although not necessarily limited thereto, the present invention is especially useful in conjunction with large overhead doors such as are typically employed in garages, warehouses and the like.
Powered overhead doors have been extensively adopted for a wide variety of uses. The hazards associated with such power doors have been recognized for some time and thus there have been a variety of efforts directed toward developing warning systems to prevent injury to persons and/or property as a result of impacting a door in motion. A typical such system is shown in U.S. Pat. No. 2,758,836 by Purdy wherein a warning light is associated with the motor drive mechanism employed in conjunction with an overhead door. A generally similar approach was earlier suggested in U.S. Pat. No. 1,951,905 by Hansen. A primary disadvantage of such systems is that they are generally only operative during such periods of time as power is being applied to the door drive mechanism. Thus, they are effective to warn those in the vicinity while the door is moving but do not provide any warning in the event that the door is actually stopped in other than its maximum limit positions. This means that an overhead door which has stopped below a predetermined limit for a vehicle would not result in any warning to a vehicle operator who may impact the door believing that sufficient clearance existed. An apparatus for indicating proximity of a metal body to sides of a device is shown in U.S. Pat. No. 3,493,925 by Brancale but such an arrangement is not well suited for detecting intermediate door stop positions for overhead doors.
A variety of magnetically operated switch proximity detectors have also been developed in the past. For instance, various applications of magnetically closed reed switches are generally shown in U.S. Pat. Nos. 3,648,817 by Siegel; 3,251,962 by Jones; 3,623,585 by Mason; 3,710,369 by Takahashi and 2,624,792 by Fruh. However, none of the magnetically operated switch devices are well suited for use in environments which can only accommodate relatively loose magnetic circuit couplings as in commercial overhead door installations.